1. Field of the Invention
The invention relates to a receiver including means for acquisition and comparison of signals from a first and a second channel of which at least the signals from the first channel, referred to as current channel, comprise a repetitive group of N data (N positive integral) particularly having its own identification code and at least a tuning search indication for searching said second channel, referred to as alternative channel, said receiver being tuned to the current channel whose identification code has been stored.
2. Description of the Related Art
An example of a channel as described above is known from the publication by the "European Broadcasting Union (EBU) no. 3244-F p. 11" in which the RDS system is described. This publication is herein incorporated by reference.
The RDS system is conceived in such a way that the car radio of a listener who is travelling can be automatically tuned permanently to the best transmitter transmitting the program selected by the listener.
Page 29 of the above-cited document states various known methods of "search tuning", i.e. searching an alternative transmitter whose channel is different from that of the transmitter which is being listened to, i.e. the so-called actual transmitter.
The installation of the RDS system is neither universal nor obligatory, nor is it immediately certain which aspects should be taken into account by the manufacturer of a car radio which is suitable for the RDS system, because there is a multitude of transmitters only some of which are provided with the RDS system at the transmitter end.
The invention is only applicable if the actual or current transmitter transmits in accordance with the RDS system, i.e. with a program identification code (PI code as indicated on page 12 of the above-cited document) and with at least an alternative frequency indication (AF code in a group of the OA type as indicated on page 16 of the above-cited document).
The technical problem posed by searching an alternative channel whose frequency is known and whose reception quality is better than that of the current channel because of the higher field strength is that, before substituting the alternative channel for the actual one, it is necessary to ensure that the program on the alternative channel corresponds to the program on the current channel. A vehicle which moves away simultaneously from a current channel transmitter and an alternative channel transmitter may capture a third channel transmitter whose frequency is equal or proximate to the frequency of the alternative channel but which does not transmit the same program.
The invention has for its object to effect an identity check before changing stations, which check takes place while the listener is listening to the current or actual program, without an annoying interruption of this program.
Page 29 of the above-cited document proposes 3 solutions, but none of them is satisfactory for a receiver comprising only one "RF input stage", i.e. a single tuner.
During acquisition of the identification code of the alternative channel it is either possible to mute the audio section of the receiver and in this case the listener is subjected to unpleasant periods of silence, or it is possible to keep the audio section in an active state, which may involve the risk that the listener is subjected to constant program changes, which will be the case in big cities with numerous local radio stations in a relatively small geographical area.
The invention has for its object to overcome this drawback.